The present invention relates to a method for providing enteric or enterosoluble coating on solid dosage forms or, more particularly, to a method for providing enteric coating on solid dosage forms by use of an aqueous coating liquid.
As is well known, enteric-coated solid dosage forms are in general prepared by use of a coating solution or liquid with an organic solvent as the solvent or dispersing medium. The use of such an organic coating liquid is sometimes undesirable since the use of large amounts of organic solvents always involves problems of a danger of explosion or fire hazards and a health problem of workers if not to mention the increased cost inherent to the solvent per se as well as the cost caused by the investment for the facilities for the recovery of the solvent or prevention of air and sewage pollution by the organic solvent.
It has been therefore a long-desired problem to be solved in the pharmaceutical technology to develop a method for providing enteric coating on solid dosage forms by not using a coating liquid with an organic solvent. Various attempts have been made in this direction according to which a finely divided coating material is dispersed or suspended in a medium of water or a mixed solvent of water as the main component and ethyl alcohol to give a coating liquid.
One of the problems in the use of an aqueous coating liquid is that addition of certain kinds of additives such as a stabilizing agent and an auxiliary solvent is indispensable in order to improve the stability of the coating liquid while these additives canot be free from the problem of their own toxicity, especially, when they remain in the coating layer on the entericcoated solid dosage forms. Thus no satisfactory method has yet been established in which the above described problems in the prior art are completely solved.